The enzyme C.sub.17-20 lyase cleaves the 17-20 carbon-carbon bond in steroids having a carbon substituent at the 17.beta.-position and serves to convert such steroids into the precursors of testosterone, 5.alpha.-dihydrotesterone and estrogens. Compounds which inhibit this enzyme would thus serve to inhibit formation of the indicated precursors and would thus be useful in the treatment of various androgen and estrogen dependent disorders. Such treatments would not be limited by the origin of the precursor. Thus, for example the formation of androgens in the adrenal glands would also be inhibited, which is ordinarily not true with regard to other treatments. More specifically, such enzyme inhibitors would be useful in the treatment of prostatic carcinoma, prostatic hyperplasia, virilism, congenital adrenal hyperplasia due to 21-hydroxylase deficiency, hirsutism and estrogen dependent breast tumors. Thus, for example, it is well established that reduction of serum testosterone levels is useful in the treatment of many cases of prostatic carcinoma. In clinical practice, this has been accomplished by orchiectomy or by diethylstilbestrol treatment but the first approach is often psychologically unacceptable while a number of side effects are associated with the second approach. Thus, an alternative approach to testosterone reduction is desirable and this can be accomplished by the administration of compounds which are lyase inhibitors. To the extent that prostatic carcinoma is androgen-dependent and breast tumors are estrogen-dependent, such inhibitors would block the indicated source of androgens or estrogens and thus provide an appropriate treatment for the indicated condition.